<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>AJAX基础回顾</title>
</head>
<body>
  <script>

    var xhr = new XMLHttpRequest()
    xhr.open('GET', 'test.php')
    xhr.send()
    xhr.onreadystatechange = function () {
      if (this.readyState !== 4) return
      console.log(this)
    }

  </script>
</body>
</html>
